Field of the Invention
This invention relates to a hydrostatic axial piston machine utilizing a bent-axis construction having a drive shaft located inside a housing so that it can rotate around an axis of rotation, a drive flange located inside the housing so that it can rotate around an axis of rotation, and a cylinder barrel located inside the housing of the axial piston machine so that it can rotate around an axis of rotation. The cylinder barrel has a plurality of piston bores, in each of which is located a longitudinally displaceable piston. The pistons are fastened to the drive flange in an articulated manner by ball joint connections formed by a spherical cap-shaped receptacle socket in one end surface of the drive flange and a ball head in an operative connection with the piston.
Description of Related Art
In hydrostatic axial piston machines utilizing a bent-axis construction, the longitudinally displaceable pistons located in the cylinder barrel are generally fastened to the drive flange of the drive shaft by a ball joint. The piston forces are transmitted by the piston to the drive flange located on the drive shaft and generate a torque. In axial piston machines utilizing a bent-axis construction, it is necessary to fasten the pistons to the drive flange in an articulated manner. For this purpose, a ball joint connection is used that consists of a spherical cap-shaped receptacle socket in one end surface of the drive flange and a ball head located on the piston and inserted into the receptacle socket of the drive flange.
In operation, the ball heads of the pistons must be held in place in the respective receptacle sockets of the drive flange.
WO 2004/109107 A1 describes a hold-down plate with openings for the piston heads and spherical caps formed on the openings threaded over the pistons and bolted to the drive flange.
Because of the need for the hold-down plate, which is complex and expensive to manufacture on account of the spherical caps and the threaded connectors that are required to bolt the hold-down plate to the drive flange, axial piston machines of this type are complex and expensive to construct.
To eliminate the effort required for the construction of the additional hold-down plate, EP 0 567 805 B1, EP 1 071 884 B1, DE 40 24 319 A1 and EP 0 697 520 B1 teach that the ball heads can be positively secured in the spherical cap-shaped receptacle sockets. The spherical cap-shaped receptacle socket has a wrapping angle greater than 180 degrees, so that the receptacle sockets wrap around the ball equator, and the ball heads have a cylindrical surface area, e.g., by flattening or machining of the ball head, so that the ball head is inserted into the spherical cap-shaped receptacle socket in a defined position by the cylindrical surfaces, and can then be secured in the receptacle socket by tilting. The manufacture of the components is thereby simplified and makes possible an easy assembly of the pistons with the ball heads in the receptacle sockets of the drive flange.
In EP 0 567 805 B1 and EP 1 071 884 B1, the cylindrical surfaces are oriented parallel to the longitudinal axis of the pistons so that during assembly, the pistons are threaded into the receptacle sockets coaxially to the axis of rotation of the drive flange. When the pistons are tilted to the working angle, the piston heads are locked in position in the receptacle shells. In bent-axis machines in the form of variable displacement machines, when the pistons are locked in position in the receptacle sockets in this manner, the coverage of the ball heads in the receptacle sockets can become too small as the pivoting angle of the cylinder barrel decreases. Thus, these methods of locking the ball heads of the pistons in the drive flange are suitable only under certain conditions for use in variable displacement machines with a variable pivoting angle of the cylinder barrel. These locking mechanisms are not suitable for use in variable displacement machines with a pivoting angle of 0° because the pistons can no longer be securely held in the receptacle sockets and can fall out of the receptacle sockets.
In DE 40 24 319 A1 and EP 0 697 520 B 1, the cylindrical surfaces are oriented at an angle with respect to the longitudinal axis of the pistons. The angle of inclination of the cylindrical surfaces is such that this angle does not occur during operation of the axial piston machine. Therefore, this locking mechanism is suitable for use on variable displacement machines and makes it possible to lock the pistons in the receptacle sockets of the drive flange even at a pivoting angle of 0°. For the installation of the pistons in the drive flange, the pistons must be tilted sharply, in which case it may be necessary to provide a recess (which is complex and expensive to manufacture) on each receptacle socket as an opening or recess for the piston rod of the piston. Depending on the installation angle of the pistons, this recess in the receptacle socket of the drive flange necessary for the installation of the pistons can extend to the equator of the ball, as a result of which the surface area of the spherical cap-shaped receptacle socket is significantly reduced.
In the axial piston machines described in EP 0 567 805 B1, EP 1 071 884 B1, DE 40 24 319 A1 and EP 0 697 520 B1, as a result of the wrapping angle of more than 180° of the spherical cap-shaped receptacle sockets, there is a correspondingly high thickness of the drive flange. This takes up a correspondingly large amount of space in the axial direction of the axial piston machine because the rotating cylinder barrel with the end surface containing the piston outlet openings may not come into contact with the end surface of the drive flange in which the receptacle sockets are located.
Therefore, it is an object of this invention to provide an axial piston machine utilizing a bent-axis construction in which the locking of the pistons in the drive flange is easier to manufacture and makes it possible to reduce the axial dimensions of the axial piston machine.